Hearing loss is a prevalent and chronic health condition that affects between 22 and 28 million Americans. Among children, premature neonates have the highest prevalence rate of sensorineural hearing loss, which is strongly associated with perinatal exposure to ototoxic agents. Our long-term goal is to identify safe and simple otoprotective strategies that could prevent sensorineural hearing loss secondary to exposure to ototoxic agents. The primary site of action of most ototoxic agents is the mitochondria, with cochlear damage resulting from cell necrosis and apoptosis. Few protective strategies aimed at decreasing mitochondrial damage have been studied. In preliminary experiments, we found that the natural micronutrient L-carnitine (LCAR), which is required for normal mitochondrial function, prevented perinatal cisplatin-induced sensorineural hearing loss and cochlear damage in guinea pigs. We hypothesize that LCAR, a safe agent in humans, can decrease drug-induced ototoxicity in the guinea pig model. Specific Aims: a) For both adult and newborn guinea pigs, to determine if LCAR supplementation can prevent sensorineural hearing loss and cochlear damage induced by gentamicin or kanamycin administered during the perinatal period. b) To determine if LCAR can decrease the toxic effects of cisplatin, gentarnicin, neomycin, streptomycin or kanamycin on cultured auditory cell lines. Design/Methods: We propose to determine the in-vivo and in-vitro otoprotective effect of LCAR. a) In-vivo studies: Gentamicin and kanamycin will be used as ototoxic agents during the guinea pig perinatal period in order to mimic late gestational exposure, when maximum cochlear development of the guinea pig fetus resembles that of the human premature neonate. Post-treatment sensorineural hearing loss will be evaluated in the adult and newborn guinea pigs by auditory brainstem responses (ABR) to clicks. Morphological cochlear damage will be assessed by confocal and electron microscopy. b) In-vitro studies: a cultured auditory cell line will be exposed to cisplatin, gentamicin, neomycin, streptomycin or kanamycin, with and without pre-incubation with different concentrations of LCAR. Fibroblastic NlH3T3 cells will be used as control. Cellular necrosis and apoptosis will be assessed by caspase assay and cellular DNA fragmentation. We are confident that accomplishing these aims will provide critical information for the development of simple intervention strategies aimed at preventing ototoxic drug-induced sensorineural hearing loss that could be used in humans, including newborns.